It may be perception about fuel economy, but in reality is it that much different? We had a 1984 49' Gulfstar MY with a similar semi-displacement hull as the our 53 Hatteras. It got about the same fuel economy with 350hp Perkins turbo V-8's as we get with the 465hp 6v92's in the Hatteras. Both could get 1nm/gal at 9kts and about 1/2nm per gal at 16kts. Maybe the newer engines are better, but with these deals on older boats, you'd never burn enough fuel to make up for the added initial cost.
People get this anti Detroit hysteria, They are still very reliable engines and relatively inexpensive to own. The1000hr service on a Man or MTU start @ 25,000.00
The Gilkes Raw water pump on the MTU is 5,000.00 and is not considered rebuildable.......
The 1500 hr rebuilds on Detroits are because people do not like the cold start smoke, they still make power and run fine even with low compression. You can run them for years even worn out. I know of numerous 92 series that has 4000+ hours in pleasure craft that are still going.
On many of the more "modern" mechanical engines the smoke at the dock will run you out and it is considered normal. I know someone who has 2 huge industrial fans on the seawall for when he lights off his V12 MTU's.
Of course the electronic engines don't smoke and can do things the mechanicals can't do, but is it really worth six figures to replace something that works fine.
Last year I took a 1990 48 Viking on a 2800 mi trip. The boat has 760 HP 8V92 TA DDEC in it, ran at 1775 rpm making 24+ knots. Got .5 MPG consistently. I would double the mileage and that was the fuel burn.
When I got home there was an article about another 48 Viking that was just repowered with Cummins, the Cummins boat ran 1 kt slower at cruise and got .5 MPG. Other than new modern engines I do not see any gain there.
Of course people are buying the Smart Car for 15,000 and the Prius that Toyota loses money on and has a very expensive battery in it that will have to be factored into the cost. If you buy a 30 mpg regular car I think you come out ahead. People blindly buy into what they are told.